1. Field of the Invention
This invention relates to a liquid jet device for exhausting and flying liquid drops through an orifice in accordance with an electrical signal and to a liquid jet recording apparatus provided with the same.
2. Description of the Prior Art
In a liquid jet recording apparatus, the open system supply mechanism as shown in FIG. 1 of the accompanying drawings is possible in principle as a feature thereof. That is, in a system filled with recording liquid (so-called ink) from a tank (liquid reservoir) 103 having a vent hole 104 so as to always maintain the pressure within the tank at the atmospheric pressure to a recording head 101 through a supply passageway 102, the amount of decrease of the recording liquid exhausted as liquid drops 105 from the end of the head 101 (exhaust orifice) in accordance with an electrical signal applied to the recording head 101 may be successively replenished to the end of the head 101 by the surface tension of the liquid. However, where such a system is applied to various recording apparatuses, there occur various problems. First, when the apparatus body is inclined, a height difference (level difference) occurs between the tank 103 and the exhaust orifice due to some degree of distance present from the tank 103 to the end of the head 101 and the meniscus of the recording liquid formed by the exhaust orifice may be retracted toward the supply passageway or conversely, the liquid may leak from the exhaust orifice. Accordingly, in case of the retraction of the meniscus, the meniscus can be recovered as by pressing the liquid from the tank 103 side, but in the case of the leakage, the interior of the apparatus is stained with the liquid. Such inclination often occurs during transportation or movement of the apparatus and frequently occurs in the case of, for example, a desk-top type calculator or a small typewriter. Therefore, if the recovery of the retracted meniscus must be effected or the interior liquid leaks each time the apparatus is moved, such apparatus cannot be a practical product.
Also, when agitation or impact is imparted to the apparatus, the leakage of the liquid and the retraction of the meniscus resulting from said inclination of the apparatus are accelerated. That is, when an extraneous stress such as agitation or impact is applied to the apparatus body or the supply passageway 102, the meniscus in the exhaust orifice is readily destroyed by such extraneous stress and the liquid is exhausted outwardly as liquid drops or the meniscus is retracted. At this time, when the apparatus is in its inclined condition, namely, when there is a level difference, the once destroyed meniscus cannot readily restore its original condition but may continuously leak outwardly or may be retracted in the supply passageway to a position in which a balanced condition may be maintained. Such agitation or impact usually frequently occurs, and always occurs particularly in the case of an apparatus in which the recording head 101 is reciprocally moved relative to a recording medium to effect recording.
A further important problem to be solved is that when recording is effected with the recording head being reciprocally moved at high speed relative to a recording medium such as paper or the like as in a small printer, the supply passageway is vibrated following the movement of the head 101 with a certain point on the tank 103 side as a fulcrum. At this time, the liquid contained in the supply passageway 102 is subjected to the influence of centrifugal forces, and the centrifugal forces so applied increase as the mass of the liquid contained in the supply passageway 102 is greater or the speed of the reciprocal movement is greater. When these centrifugal forces overcome the retention force of the meniscus, the liquid is caused to flow out through the exhaust orifice even if a print signal is not applied to the recording head. This means that the apparatus and the recording medium are stained with the liquid, and it is a fatal drawback in practice.
To avoid such inconvenient phenomenon resulting from the reciprocal movement of the recording head portion during recording, liquid jet devices designed so that the recording head portion and the tank portion (liquid reservoir portion) are moved together are disclosed, for example, in U.S. Pat. No. 3,953,862, U.S. Pat. No. 3,967,286 and U.S. Pat. No. 4,095,237.
To overcome the above-noted inconvenience, the liquid jet devices disclosed in these patents are not only designed so that the recording head portion and the liquid reservoir portion are moved together, but also improved so that when the device is reciprocally moved during recording, the liquid may not leak from a vent hole provided in the liquid reservoir portion as the result of the vibration of the liquid in the liquid reservoir portion caused by the acceleration and deceleration or air may not be mixed with the liquid.
However, in the liquid jet devices having constructions as disclosed in these prior arts, the positional relation between a liquid chamber for producing the motive power of the requid jet of the recording head portion and the liquid level in the liquid reservoir portion is random, so that the exhaust of the liquid becomes unstable with the lowering of the level of the liquid in the liquid reservoir portion and the supply of the liquid to the liquid chamber cannot be accomplished smoothly and speedily, and the probability with which the supply passageway is clogged is high because a portion of such liquid passageway from the liquid reservoir portion to the liquid chamber lies below the bottom surface of the liquid reservoir portion, and when the supply passageway is clogged, it is difficult to repair the clogged portion. Thus, the devices according to the prior art should be improved in these points.
It will thus be understood that from these practical problems, it is very difficult for the open system supply mechanism which is possible in principle to be applied to an actual recording apparatus.
In contrast, there is a liquid jet recording apparatus having a so-called hermetically sealed system supply mechanism. As shown in FIG. 2 of the accompanying drawings, this system has a pressurizing mechanism 205 in a tank 203 and adopts a method whereby the amount of decrease of the liquid exhausted from a head 201 is replenished by opening-closing of a valve 206 provided in a supply passageway 202, or the tank 203 is designed similarly to the tank 103 of FIG. 1, namely, such that the internal pressure of the tank is identical to the atmospheric pressure and the tank 203 is provided with no special pressurizing mechanism but a pressurizing mechanism is provided in the valve 206. The opening-closing of the valve 206 may be accomplished in accordance with a signal from a liquid amount detector such as a pressure sensor provided adjacent to the head 201 or in the supply passageway 202. The portion from the valve 206 to the head 201 can be considered to be a hermetically sealed system and therefore, the aforementioned problems occurring to the open system may be considerably reduced. However, this hermetically sealed system supply mechanism, as will be appreciated from the simple illustration of FIG. 2, requires a complicated mechanism and involves a considerable cost and cannot make the best use of its characteristics.
The inventors have analyzed the problems peculiar to the open system supply mechanism and as a result, could develop a liquid jet recording apparatus which is very simple in construction and which has a practically sufficient printing stability and reliability.